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Flexible and rechargeable Zn–air batteries, because of their high energy density, low cost, and environmental and human benignity, are one kind of the most attractive energy systems for future wear...

Pyrolyzed base-metal-based metal-organic frameworks (MOFs) with FeNx coordination are emerging as nonprecious metal catalysts for electrochemical oxygen reduction reaction (ORR). However, surprisingly, nonpyrolyzed MOFs involving Fe-N coordination have not been explored for the ORR. This study concerns the catalytic performance of a semiconducting nonpyrolyzed iron triazolate framework (FeTa2 ) for ORR in alkaline electrolyte. The FeTa2 catalyst is studied as composites with different amounts of conductive Ketjenblack carbon (KB). The performance of these FeTa2 -x KB (x denotes the KB/FeTa2 weight ratio) composites by onset and half-wave potentials of ORR appears to be superior to most previously documented nonpyrolyzed MOFs. Characterization by elemental analysis, FTIR spectroscopy, XPS, and cyclic voltammetry suggest that N-FeIII -OH- sites at the surface of FeTa2 function as the catalytic active sites. This FeTa2 also shows very stable activity during ORR, as supported by accelerated durability test of the FeTa2 -x KB sample (20 000 cycles, ca. 90 h). The framework structure of FeTa2 remains intact during the durability test, which would help to explain its excellent catalytic durability. This would be the first study demonstrating efficient and stable ORR catalysis by a nonpyrolyzed Fe-N coordination-based MOF material.

Controlled synthesis of highly efficient, stable, and cost-effective oxygen reaction electrocatalysts with atomically-dispersed Me-Nx -C active sites through an effective strategy is highly desired for high-performance energy devices. Herein, based on regenerated silk fibroin dissolved in ferric chloride and zinc chloride aqueous solution, 2D porous carbon nanosheets with atomically-dispersed Fe-Nx -C active sites and very large specific surface area (≈2105 m2 g-1 ) are prepared through a simple thermal treatment process. Owing to the 2D porous structure with large surface area and atomic dispersion of Fe-Nx -C active sites, the as-prepared silk-derived carbon nanosheets show superior electrochemical activity toward the oxygen reduction reaction with a half-wave potential (E1/2 ) of 0.853 V, remarkable stability with only 11 mV loss in E1/2 after 30 000 cycles, as well as good catalytic activity toward the oxygen evolution reaction. This work provides a practical and effective approach for the synthesis of high-performance oxygen reaction catalysts towards advanced energy materials.

Iron and nitrogen co-doped carbon (Fe-N-C) materials are among the most active non-precious metal catalysts that could replace Pt-based electrocatalysts for the oxygen reduction reaction (ORR) in fuel cells and metal–air batteries. The synthesis of the Fe-N-C catalysts often involves the use of aniline as the precursor for both N and C and ammonium peroxydisulfate (APS) as an indispensable oxidative initiator for aniline polymerization. Herein, a detailed structure and catalytic ORR performance comparison of aniline-derived Fe-N-C catalysts synthesized with and without the use of APS is reported. The APS-free preparation, which uses FeIII ions as the Fe source as well as the aniline polymerization initiator, results in a cleaner and simpler Fe-N-C catalyst with a higher activity for the ORR. We show that APS is not necessary for the preparation and even detrimental to the performance of the catalyst.